Ultraviolet Photoconductive Detector Research Articles

Micro spot ZnO nanotubes using laser assisted chemical bath deposition: A low-cost approach to UV photodetector fabrication

Due to its outstanding characteristics across a wide variety of applications, such as electrical, photonic, electrochemical, and electromechanical devices, one-dimensional Zinc oxide (ZnO) is one of the most promising nanostructures. Using a continuous wave semiconductor laser with a wavelength of 460 nm and a power of 1 W, functional ZnO nanostructures known as nanotubes (NTs) with high-quality structural, optical, and electrical properties on a glass substrate coated with iron (Fe) to construct a UV photoconductive detector with high responsivity were produced for first time by using a simple and quick laser assisted chemical bath deposition (LACBD). X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive X-ray (EDX)analyses were used to investigate the evolution of the material's physical and structural characteristics. Our findings revealed that laser-assisted in-situ irradiation of the chemical solution resulted in faster growth of ZnO thin films. To account for the potential of these nanostructures, the effectiveness of ZnO nanotubes (NTs) in ultraviolet (UV) detection has also been investigated. The NT-based photodetector has outstanding stability and responsiveness in both dark and light conditions. Exciton confinement is identified using time-resolved spectroscopy, suggesting that the high surface-to-volume ratio, optical confinement, and high structural quality of the NTs are responsible.

Vacuum ultraviolet photoconductive detector based on anatase TiO2 thin film deposited on SiO2 substrate

We report on titanium dioxide (TiO2) thin film deposited on a quartz (SiO2) substrate as an improved photoconductive detector for radiation below 200 nm wavelength (vacuum ultraviolet region, VUV). The crystalline film has an anatase phase and an average crystallite size of 10.6 nm. It has a transmission edge at 322 nm and an optical band gap of 3.18 ± 0.02 eV. Under VUV illumination, the TiO2 photoconductive detector exhibited a photocurrent of 5.3 mA at an applied bias voltage of 100 V. The dark current measured without VUV illumination and at the same bias voltage is 8.8 × 10−6 mA, which is 6 orders of magnitude smaller compared to the photocurrent. The photoconductive VUV detector based on TiO2 thin film provides a means of directly measuring VUV radiation compared to detection via the photoluminescence of a scintillator.

Effect of Substrate and Thickness on the Photoconductivity of Nanoparticle Titanium Dioxide Thin Film Vacuum Ultraviolet Photoconductive Detector.

Vacuum ultraviolet radiation (VUV, from 100 nm to 200 nm wavelength) is indispensable in many applications, but its detection is still challenging. We report the development of a VUV photoconductive detector, based on titanium dioxide (TiO2) nanoparticle thin films. The effect of crystallinity, optical quality, and crystallite size due to film thickness (80 nm, 500 nm, 1000 nm) and type of substrate (silicon Si, quartz SiO2, soda lime glass SLG) was investigated to explore ways of enhancing the photoconductivity of the detector. The TiO2 film deposited on SiO2 substrate with a film thickness of 80 nm exhibited the best photoconductivity, with a photocurrent of 5.35 milli-Amperes and a photosensitivity of 99.99% for a bias voltage of 70 V. The wavelength response of the detector can be adjusted by changing the thickness of the film as the cut-off shifts to a longer wavelength, as the film becomes thicker. The response time of the TiO2 detector is about 5.8 μs and is comparable to the 5.4 μs response time of a diamond UV sensor. The development of the TiO2 nanoparticle thin film detector is expected to contribute to the enhancement of the use of VUV radiation in an increasing number of important technological and scientific applications.

Titanium dioxide thin films as vacuum ultraviolet photoconductive detectors with enhanced photoconductivity by gamma-ray irradiation

We show that titanium dioxide (TiO2) thin films can be used as photoconductive detectors of vacuum ultraviolet (VUV) radiation, with further improvement in performance after recovery from gamma ray irradiation. An initial decrease in photocurrent was observed after irradiation with 3.4 kilo gray gamma rays as oxygen vacancies and trivalent titanium ion states are formed as confirmed by optical and photoluminescence spectroscopies showing a red-shift in the transmission edge, narrowing of the optical band gap, and appearance of a broad absorption band in the 392-528 nm wavelength range. Subsequent recovery of these defects increased the photoconductivity beyond what was displayed by the pristine detector. After recovering, the photosensitivity of the detector increased by a factor of about 8 and 124 compared to its photosensitivity before and immediately after irradiation, respectively. As the applications of VUV light continue to grow and development of light sources progress, there is increased demand for detectors in this short wavelength region. Our results demonstrate the potential of TiO2 thin films as VUV detectors including the use of gamma ray irradiation as post-fabrication treatment for improved photoconductivity.

Ultraviolet Photoconductive Detector Based on MgO/a-GaN Heterostructure Grown by Aqueous Method.

Thin MgO nanostructure layer was grown on a-plane GaN film in this study using low temperature aqueous method. The thin MgO layer showed uniform sheet-like morphology. Meanwhile, ultraviolet (UV) photoconductive detector based on MgO/a-GaN heterostructure was fabricated by simple way. The obtained detector displayed excellent UV sensing properties. Results showed that the thin MgO nanostructure layer can effectively decrease the dark current and passivate the surface defects. The facile method will provide a new route to adopt nanostructures for applications in enhancing the performance of GaN-based UV detector.

Filterless tunable photoconductive ultraviolet radiation detector using CeF3 thin films grown by pulsed laser deposition

We report the development of filterless deep ultraviolet photoconductive detectors using cerium fluoride (CeF3) thin films fabricated by pulsed laser deposition (PLD). By varying the PLD laser power during thin film growth, we observed that CeF3 breaks down to CeF2 at PLD laser powers greater than 100 mW. This consequently leads to the formation of fluorine defects that effectively narrowed the optical bandgap of the thin films, resulting in the decreased resistivity of the photoconductive detector. Under ultraviolet irradiation, the detector using a thin film grown at 5 mW PLD laser power exhibited close to four orders of magnitude increase in photocurrent compared to the dark current. The spectral response of the photoconductive detectors can be tuned from 300 nm to 400 nm when PLD laser powers ranging from 5 mW to 400 mW are used to fabricate the thin films. The filterless nature of the detectors simplifies their production, and their tunability can extend their use to a wider range of applications.

Band gap engineering of CaxSr1-xF2 and its application as filterless vacuum ultraviolet photodetectors with controllable spectral responses

We experimentally demonstrate that the band gap of mixed crystals of calcium fluoride and strontium fluoride (CaF2 – SrF2, CaxSr1-xF2) can be engineered by modulating the composition ratio of CaF2 and SrF2. By increasing the CaF2 content, the band gap increases and the absorption edge is blue-shifted. A range of band gap energies can be obtained between 9.73 eV for pure SrF2 and 10.24 eV for pure CaF2. The first order Raman frequency shift increases linearly from 285.2 cm−1 for pure SrF2 to 327.8 cm−1 for pure CaF2. The ability to manipulate the band gap is maintained even at very low temperatures. Vacuum ultraviolet (VUV) photoconductive detectors are fabricated to explore the effect of varying composition ratios on spectral sensitivity. The spectral response of the photodetectors shifts to shorter wavelengths as the band gap increases. This allows the spectral response to be controlled by appropriately choosing the CaF2 – SrF2 ratio. Using CaxSr1-xF2 sensors also eliminates the need for extra filters to cut off unwanted longer wavelengths as the onset of their absorption occur in the VUV region. The controllable spectral response and filterless feature of CaxSr1-xF2 photodetectors provide an advantage over currently available oxide-, nitride-, and diamond-based photodetectors.

Chemical synthesis of pinecone like ZnO films for UV photodetector applications

Highly selective metal-semiconductor-metal (MSM) Ultra-Violet (UV) photodetectors were successfully demonstrated based on pinecone shaped zinc oxide (ZnO) films. The pinecone shaped ZnO photodetectors were synthesized via successive ionic layer by adsorption and reaction method (SILAR). The MSM device with silver (Ag) as contact electrode, possess simplicity in material synthesis and advantages in the device design and testing. Morphological evolution using SILAR method involves Ostwald's ripening process. The field emission scanning electron microscopy (FESEM) study reveals the formation of pinecone like ZnO structure with high surface area for adsorption of oxygen molecules. The device exhibited good photoresponse and spectral responsivity under ultraviolet (UV) illumination (power density 1.8μWcm−2) at 5V bias voltage. At 365nm wavelength, the highest peak responsivity observed was 350.98A/W. The device showed good ohmic contact between metal semiconductor junctions. Our finding provides new route for the fabrication of low cost and highly selective UV photoconductive detectors.

High-performance visible blind ultraviolet photodetector based on KTaO3 single crystal.

We report a visible-blind ultraviolet photoconductive detector with interdigitated electrodes based on KTaO3 (KTO) single crystals. Both the steady spectral responses and the transient photovoltaic measurements clearly exhibit a cutoff wavelength at 344 nm (∼3.6 eV), in accordance with the bandgap of KTO. The KTO photodetectors show a low dark current ∼1.5 pA at 20 V, and a high UV-to-visible rejection ratio with 3 orders of magnitude at room temperature. The quantum efficiency is 37.49% under 20 V bias, and the detectivity D* of 3.85×1012 cm·Hz0.5/W, which is comparable to that of silicon photodetectors in the UV region. The rise time of photoelectric response is ∼260 ps, indicating an ultrafast photoelectric response characteristic. The present work offers appealing prospects for the application of KTO materials in high-performance visible blind ultraviolet photodetectors.

Chemical bath deposited ZnO thin film based UV photoconductive detector

Ag/ZnO/Ag metal-semiconductor-metal (MSM) Ultraviolet (UV) photodetectors based on Zinc oxide (ZnO) thin films are successfully fabricated on the glass substrate by using chemical bath deposition (CBD), which shows the good ohmic contact behavior between metal-semiconductor junctions. The devices are characterized to investigate the effect of deposition time and thickness on the photoconductive properties of ZnO thin films. The physiochemical properties of ZnO thin films are carried out. Thin films exhibit hexagonal crystal structure with the preferential orientation along (002) plane. With the applied bias of 5 V, the ZnO based photodetector shows low dark current and high photocurrent of 113.83 μA. The device exhibits relatively high photoresponse with rise time about 9 s and fall time about 21 s. It suggests that ZnO thin films are potential candidates for the UV photodetector application using easy and low-cost fabrication method.

Ultraviolet Photoconductive Detectors Based on A-Plane ZnO Film Grow by Hydrothermal Method

A-plane ZnO film was grown on a-plane GaN/r-sapphire template by using the hydrothermal growth method. The film was characterized for the structural and morphological properties by means of x-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results show the a-plane ZnO film with a very uniform striated morphology was achieved. Meanwhile, an ultraviolet (UV) photoconductive detector based on the as-grown a-plane film was fabricated, and the detector current was increased by more than 17 times under 5 V bias upon UV illumination. Moreover, it also showed good reproducibility and stability, which confirms the film as a good potential material for UV optoelectronic devices.

ZnO/Ag nanowires composite film ultraviolet photoconductive detector**Project supported by the National Natural Science Foundation of China (Nos. 61176056, 91323303, 91123019), the 111 Program (No. B14040), and the Open Projects from the Institute of Photonics and Photo-Technology, Provincial Key Laboratory of Photoelectronic Technology, Northwest University, China.

ZnO/Ag nanowires (NWs) film ultraviolet (UV) detector was fabricated by a simple and low-cost solution-processed method. In order to prepare this device, Ag NWs network was first spin-coated on glass substrate as a transparent conducting electrode, then ZnO NWs arrays were grown vertically on the Ag NWs network based on the hydrothermal method. This UV detector exhibited an excellent detection performance with large on/off ratio and short response time. Several process and working parameters were particularly investigated to analyze the relationship between structure and performance, which include growth time of ZnO NWs array, spin speed of Ag NWs network and working temperature. This UV photoconductive detector is based on two kinds of one-dimension nanomaterials, and it was regarded as a compromise between high performance with large area, low voltage and low cost.

Development of 2-D Boron Nitride Nanosheets UV Photoconductive Detectors

We report on our new approach to low-temperature synthesis of high-quality single crystalline wide bandgap boron nitride nanosheets (BNNSs) semiconductor for the development of deep ultraviolet (UV) photoconductive detectors. We focus our experiments on studies of electrical and electronic properties, as well as sensitivity, response and recovery times, and repeatability of newly fabricated deep UV detectors. Raman scattering spectroscopy, X-ray diffraction, scanning electron microscope (SEM), transmission electron microscopy (TEM), and electrometers were used to characterize the BNNS photoconductive materials. The SEM and TEM measurements clearly indicate that each sample consists of a large amount of high-quality BNNSs. High transparency related to high quality of crystalline structures of BNNS has been identified. Based on the synthesized BNNSs, deep UV detector is designed, fabricated, and tested. High sensitivity, quick time responsivity <0.6 ms has been achieved.

Vacuum ultraviolet photoconductive detector based on pulse laser deposition-grown neodymium fluoride thin film

A filterless vacuum ultraviolet photoconductive detector based on neodymium fluoride thin films was demonstrated. The thin films were deposited on quartz glass substrates by the pulsed laser deposition. Crystallinity and photoconductivity were improved by controlling the substrate temperature. The sample grown at 670K showed the highest photoconductivity. It responded to wavelengths shorter than 180nm without any filters.

Filterless Ultraviolet Detector Based on Cerium Fluoride Thin Film Grown by Pulsed Laser Deposition

We report on an ultraviolet photoconductive detector based on cerium fluoride (CeF3) thin films. CeF3 thin films were grown on quartz glass substrates by the pulsed laser deposition (PLD) method. Optimization of the substrate temperature using the PLD method successfully increased the photocurrent of the CeF3 detector. The photocurrent increases linearly up to at least 600 V. The sample grown at 670 K shows the highest crystallinity and orientation. This sample shows a response in the wavelength range below 310 nm without any filters. Additionally, the measured dielectric-breakdown field of this detector exceeded 15 kV/cm.

Fabrication and performance of N-doped ZnO UV photoconductive detector

We report study on the fabrication and characterization of an ultraviolet (UV) photodetectors based on N-doped ZnO films. The N-doped ZnO films with 10at% N doping are spray deposited on to alumina substrates. The photoconductive UV detector based on N-doped ZnO thin films, having a metal–semiconductor–metal (MSM) configuration are fabricated using Al as a contact metal. The dependence of I–V characteristic under dark and illumination, spectral and transient photoresponse of the detector are investigated. The linear current–voltage (I–V) characteristics under forward bias exhibit ohmic metal–semiconductor contact. The UV photoconductive effect is observed showing fast response with switching on/off UV light illumination. The neutralization of photogenerated holes by negatively charged oxygen ion plays a key role in the photoconductive characteristics of N-doped ZnO polycrystalline films.

N-doped ZnO based fast response ultraviolet photoconductive detector

We report a study on the fabrication and characterization of ultraviolet photodetectors based on N-doped ZnO films. Highly oriented N-doped ZnO films with 10 at.% N doping are deposited using spray pyrolysis technique onto glass substrates. The photoconductive UV detector based on N-doped ZnO thin films, having a metal–semiconductor–metal (MSM) configuration are fabricated by using Al as a contact metal. I– V characteristic under dark and UV illumination, spectral and transient response of ZnO and N-doped ZnO photodetector are studied. The photocurrent increases linearly with incident power density by more than two orders of magnitude. The photoresponsivity (580 A/W at 365 nm with 5 V bias, light power density 2 μW/cm 2) is much higher in the ultraviolet region than in the visible.

High-performance UV detector based on Ga-doped zinc oxide thin films

High-quality ultraviolet photoconductive detectors have been fabricated using Ga-doped zinc oxide layers grown by spray pyrolysis on glass substrates. The performance of the photoconductivity has been tested by the measurements of the current–voltage ( I– V) characteristics under forward and reverse bias. The devices have been characterized to investigate the effect of buffer layer on the detector performances. The behaviour of photocurrent with respect to optical power density, wavelength and chopping time has been investigated. We achieved the highest responsivity of about 1125 A/W at 5 V bias at 365 nm peak wavelength. Our approach provides a simple and cost-effective way to fabricate high-performance ‘visible-blind’ UV detectors.

The ultraviolet photoconductive detector based on Al-doped ZnO thin film with fast response

We report fabrication and characterization of metal-semiconductor-metal photoconductive detectors based on Al-doped ZnO thin films fabricated by radio frequency magnetron sputtering. Optical and structural properties of the thin films were characterized using various techniques. At 6 V bias, a responsivity higher than 4 A/W in the wavelength shorter than 350 nm was obtained, and this responsibility dropped quickly and reached the noise floor in the visible region. Transient response measurement revealed that the detector had a fast photoresponse with a rise time of 9 ns and a fall time of 1.2 μs.

Fast response ultraviolet photoconductive detectors based on Ga-doped ZnO films grown by radio-frequency magnetron sputtering

A metal–semiconductor–metal photoconductive detector was fabricated on c-axis preferred oriented Ga-doped ZnO (ZnO:Ga) thin film prepared on quartz by radio-frequency magnetron sputtering. With a 10 V bias, a responsivity of about 2.6 A/W at 370 nm was obtained in the ultraviolet region. The photocurrent increases linearly with incident power density for more than two orders of magnitude. The transient response measurement revealed photoresponse with a rise time of 10 ns and a fall time of 960 ns, respectively. The results are much faster than those reported in photoconductive detectors based on unintentionally doped n-type ZnO films.